Tillite (redirected from tillites)

tillite [′ti‚līt]

(petrology)

A sedimentary rock formed by lithification of till, especially pre-Pleistocene till.

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Tillite 

any one of the ancient moraines occurring as rudaceous, unsorted formations that have undergone consolidation and, sometimes, even metamorphism. Tillites are formed from a silty unstratified mass known as glacier milk; they also contain boulders bearing glacial striations.

A distinction is made between marine tillites, formed as a result of glacial transport and deposition in the sea, and continental tillites, the composition of which often provides information on the type of rock underlying the glacier and, by extension, on the ablation area and direction of the glacier. Tillites are often confused with similar rocks of nonglacial origin, for example, the deposits of mud-laden torrents and the sedimentary rock formed underwater from the deposits of turbidity currents. Tillites are testaments to periods of glaciation; they are known to have existed since the early Proterozoic era and are very widely distributed in late Proterozoic deposits on nearly all continents. Their horizons are encountered among the Upper Riphean strata of the Eastern European Platform, the Upper Ordovician regions of Africa, and the Upper Carboniferous and Permian regions of the southern continents. The thickness of tillites reaches tens and hundreds of meters.

Tillites are widely used in solving problems of stratification and paleogeography (paleoclimatology), as well as in prospecting for sedimentary minerals (iron ores). A comparison of tillites with anthropogenic moraines makes it possible to obtain a general picture of glacial sedimentation.

REFERENCE

Gretskaia, T. A: “Tillity i ikh znachenie dlia resheniia geologiche-skikh zadach.” In Itogi nauki: Seriia “Geologiia.” Moscow, 1966.

T. A. GRETSKAIA